Fast antenna calibration by orthogonal carrier sounding (facocs)

Abstract

The invention introduces a high-precision simultaneous transmitter antenna calibration method using orthogonal carrier waveforms, known as Fast Antenna Calibration by Orthogonal Carrier Sounding (FACOCS). This technique enables real-time calibration of transmitter antenna arrays, addressing phase and amplitude imbalances with exceptional accuracy. By leveraging the orthogonal properties of these carriers, the method eliminates the need for external calibration apparatus, of storage of phase or amplitude measurements for subsequent comparison, and minimizes system downtime, even for a large frequency bandwidth. It ensures optimal alignment of transmitter antennas, enhancing signal integrity and maximizing network throughput. This approach provides a robust, scalable solution for maintaining stringent calibration standards in dynamic environments, significantly improving transmitter performance and overall system efficiency.

Description

[0001] Fast Antenna Calibration by Orthogonal Carrier Sounding (FACOCS)

[0002] Field of the Invention

[0003] The present invention relates to wireless communication technology. More particularly, the invention relates to a method and system for calibrating antenna arrays in a wireless communication system.

[0004] Background of the Invention

[0005] The rapid evolution of wireless communication systems, particularly with the deployment of 5G and the development of 6G networks, has led to the widespread adoption of large-scale antenna systems like Massive MIMO (Multiple Input Multiple Output) configurations. Massive MIMO systems, which involve numerous antenna elements working in coordination, are essential to achieving enhanced capacity and improved spectral efficiency required by modern communication networks. These systems may utilize a large number of antennas to form spatially directed beams, significantly enhancing spectrum efficiency and cell capacity and allowing multiple users to be served simultaneously with minimal interference.

[0006] However, this advancement brings new challenges, one of which being the accurate calibration of the phases at the antenna elements of the array. Variations in amplitude and phase across individual radio frequency (RF) transceiver channels due to temperature variations, component aging, and operational factors can introduce incongruence among antenna phases that significantly degrade system performance, not getting expected beamwidth or sidelobe suppression of the beams. Thus, efficient and precise calibration techniques are critical for maintaining optimal system functionality.

[0007] Traditional antenna calibration is performed either over-the-air (OTA), where real-world conditions are captured from feedback from external transceivers, or internally (self-calibration), where feedback is collected from antenna ports within the system without depending on external devices.

[0008] In receive self-antenna calibration, a signal is sent over a common transmit path and is directed back through all the receive antenna paths using either switches or power splitters and a set of directional couplers, and the phases and amplitudes of the feedback are compared against that of a reference path in the time domain or in the frequency domain to estimate the calibration coefficients.

[0009] However, for transmit self-antenna calibration, if signals are sent simultaneously over multiple antennas and are monitored through a common path after collecting through directional couplers and power combiner, the signals from different antennas combine inseparably, and phases and amplitude cannot be compared.

[0010] To circumvent this issue during transmit self-calibration, signals are sent sequentially, one at a time through each antenna, which necessitates synchronization and storing, thus increasing the computation complexity and system cost. Orthogonal codes or sequences may be sent simultaneously through different antennas, but this requires separate correlators to extract the phase and amplitude of each correlation from the combined feedback. However, this is typically suitable for single-carrier systems For large bandwidth OFDM, the process of antenna calibration process needs to be repeated for narrow slices of frequency bands till the entire bandwidth is covered.

[0011] These challenges highlight the need for more innovative calibration techniques that can overcome the limitations of current methods, reduce computational complexity, and ensure optimal performance of large-scale antenna systems in evolving 5G and future 6G networks.

[0012] Object of the Invention

[0013] The objective of the invention is to enhance the simplicity and efficiency of antenna array calibration by distributing orthogonal subcarriers simultaneously through multiple transmit paths, and collecting a combined feedback from the respective antennas through a common receive path, and separating the orthogonal subcarriers for a simple phase and amplitude comparison, thereby eliminating the need for any extra circuit such as synchronization, correlation, storage, etc. of the received feedback signal.

[0014] Another objective of the invention is to enable the sounding of multiple antennas simultaneously by generating calibration signals with orthogonal subcarriers, thus speeding-up the calibration process even for a large bandwidth system and reducing the complexity associated with sequential calibration methods. Summary of the Invention

[0015] An aspect of the present invention is to address at least the above-mentioned problems and / or disadvantages and to provide at least the advantages described below. The present invention has several aspects that may be claimed and stand as patentable individually or in combination including but not limited to the following.

[0016] The invention relates to an advanced method for calibrating antenna arrays in wireless communication systems, particularly focusing on improving the calibration of multiple transmit paths. The proposed solution utilizes orthogonal subcarriers of an OFDM symbol to simultaneously transmit and differentiate signals sent through various transmit paths, ensuring accurate phase and amplitude alignment across all antennas in the array.

[0017] In one aspect of the invention is to generate a random QPSK (or higher order modulated) OFDM symbol covering the desired bandwidth and provide a calibration method for Multiple Antenna Systems in a wireless communication system by transmitting the orthogonal subcarrier sub-sets of the OFDM calibration symbol simultaneously through a plurality of transmit antennas, wherein the subcarriers are distributed into multiple transmit paths, each path carrying at least one or more subcarriers. Further, collecting feedback from two or more transmit antennas and combining the feedback into a consolidated signal.

[0018] In another aspect of the invention is to provide a calibration method for an antenna array or multiple antennas in a wireless communication system by configuring to letting the feedback from the transmitted signals from all the antennas pass through a combining circuit to form a feedback signal, which is then directed back through a common receive path, down converting the combined feedback signal and performing a Fourier transform on the down converted signal. This is followed by separating the Fourier transformed signal into subcarrier sub-sets, one of which corresponds to the reference path, against whose subcarrier subset the phases and amplitudes of the other subsets from antenna paths are compared for their calibration. To make the feedback data independent, the received subcarrier subsets are multiplied by the conjugate of the corresponding transmitted subcarrier subset. The phases and amplitudes of the data-neutralized feedback subcarriers are compared to identify transmit path mismatches. And transmission path phases and amplitudes are adjusted based on the identified mismatches to produce beams for improved throughput.

[0019] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

[0020] Brief description of the drawings

[0021] The figures described below depict various aspects of the system and methods disclosed herein. It should be understood that each figure depicts an embodiment of a particular aspect of the disclosed system and methods, and that each of the figures is intended to accord with a possible embodiment thereof. Further, wherever possible, the following description refers to the reference numerals included in the following figures, in which features depicted in multiple figures are designated with consistent reference numerals.

[0022] FIG.1(A) and 1(B) illustrate the comparison of Over the Air (OTA) and Self Calibration Techniques for Wireless Systems (100) as a reference to existing arts.

[0023] FIG. 2 depicts a configuration designed to obtain calibration symbols for an antenna array transmitting communication signals (200) in which separate receive feedback paths are used as a reference to the existing art.

[0024] FIG. 3 shows a self-calibration process for the transmit paths, mapping orthogonal subcarriers to different paths (300) in accordance with one embodiment of the present invention.

[0025] FIG. 3(A) shows a self-calibration process (300(A)) for the receive path, in accordance with one embodiment of the present invention.

[0026] FIG. 3(B-1) and 3(B-2) shows possible extensions of a self-calibration process for the transmit paths, where only a portion of antennas are calibrated at a time, especially when the number of antennas to be calibrated is very large, in accordance with one embodiment of the present invention.

[0027] FIG. 4 shows a flowchart outlining the steps for Tx calibration (400) in accordance with one embodiment of the present invention.

[0028] FIG. 5 depicts the beams formation before and after antenna calibration (500) in accordance with an exemplary embodiment of the present invention. FIG. 6 is a block diagram illustrating an example of a schematic hardware configuration of the network node (600) according to the embodiments of the present disclosure.

[0029] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

[0030] Detailed Description of the Invention

[0031] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various details to assist in that understanding but these are to be regarded as merely exemplary.

[0032] The terms and words used in the following description and claims are not limited to the bibliographical meanings but are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, the following description of exemplary embodiments of the present invention is provided for illustration purposes only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. The discussed figures and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. The principles of the present disclosure may be implemented in any suitably arranged system. It should be understood that the discussed embodiments are provided to merely aid the understanding of the description and that their use and definitions in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise.

[0033] FIG. 1(A) and 1(B) provide a detailed comparison between Over-the-Air (OTA) and self-calibration techniques for wireless systems (100). These figures highlight the differences in approach, demonstrating that OTA calibration relies on external reference signals, while self-calibration leverages internal mechanisms to perform system adjustments.

[0034] FIG. 1(A) illustrates an Over-the-Air (OTA) calibration method for wireless systems (100). In this method, the base station (BS) relies on external devices to calibrate its antenna array. The process begins with the BS transmitting calibration signals to multiple assisting mobile stations (MS) that are equipped to receive and analyze these signals. The MS devices then measure the channel state information (CSI) from the received signals and send this feedback back to the BS. The BS uses this CSI feedback to adjust and calibrate its antenna array, aiming to align the transmission and reception paths accurately.

[0035] If the MS devices are not correctly positioned or are experiencing interference or poor signal quality, the feedback may be inaccurate, compromising the calibration process. This method assumes channel reciprocity - that the channel conditions between the BS and MS are the same in both directions (uplink and downlink). However, in practical scenarios, this assumption may not always hold true due to varying conditions, such as multipath effects, fading, and environmental interference.

[0036] It also highlights the complexity and challenges associated with OTA calibration. The method requires additional hardware components, like an external transceiver (TRX), to manage the transmission and reception of calibration signals.

[0037] FIG. 1(B) depicts the self-calibration technique for wireless systems (100) where the system can calibrate itself without external references, relying only on Internal mechanisms within the base station (BS). In this approach, the BS generates calibration signals and directs them to specific antennas or groups of antennas in the array. This selective sounding allows the system to measure the response of individual antennas or antenna clusters to the calibration signals, providing precise information on the performance of each antenna element.

[0038] The diagram shows that the self-calibration method requires precise synchronization at the receiver. This synchronization accurately determines the phase and amplitude of the received signals, which are necessary for calculating the appropriate calibration factors. Unlike OTA calibration, which relies on external feedback from MS devices, self-calibration maintains complete control over the calibration process within the BS, reducing the dependence on external devices and the associated variability and uncertainties.

[0039] The wireless communication system (200) shown in Figure 2 is an example of Prior Art, that uses beamforming with multiple transmitter-receiver pairs. The system's architecture of FIG. 2 each antenna uses a unique path for Tx and Rx and does not have a common path to collect the feedback for transmit antenna calibration, which means the receive paths have to be calibrated first, which in turn needs a common path to transmit the calibration signal. This issue poses a substantial obstacle to the system's efficiency, and practical implementation in real- world wireless communication applications, potentially limiting its performance and adaptability to varying communication demands.

[0040] FIG. 3 illustrates the self-calibration process, detailing the mapping of orthogonal subcarriers to distinct paths (300) in accordance with one embodiment of the present invention. The figure shows the systematic assignment of orthogonal subcarriers to separate signal paths within the system. This mapping approach isolates each signal path, enabling easy separation and precise phase difference measurement for calibration and adjustment of the antenna system for enhanced performance.

[0041] In one embodiment, it illustrates a calibration method for an antenna array in a wireless communication system, which utilizes the simultaneous sounding of transmit antennas to overcome challenges in signal separation and calibration. This method effectively leverages the orthogonality principle of Orthogonal Frequency Division Multiplexing (OFDM) subcarriers to enable precise calibration of multiple antennas within the array.

[0042] 5 The calibration process involves picking a random OFDM symbol, generated or read off an LUT, and distributing its subcarrier, typically in a round-robin method to all the antennas (or a subgroup thereof). The distribution of the subcarriers into their respective designated paths may be done with the already existing beamforming circuit (310) by assigning ones (pass) or zeros (do not pass) as 10 coefficients.

[0043] In an embodiment of four transmit antennas, the signals in the paths may be represented as Xkwhere k varies from 0 to N - 1, which can be split into the transmit paths X4k, X4k+1, X4k+2, X4k+3, where k varies from 0 to ■■■■ 1. In the time domain they can be represented as

[0044] N__„

[0045] 4 * -15:q(n) = x4kejz^4k+0™'N

[0046] rt=Q

[0047] N_,

[0048] 41

[0049] x2(n) - X4k+1e^k+1^N

[0050] k--~0

[0051] x3(n) = y X4fc+2e;’2,l(4k+2)n / w

[0052] k~0

[0053] x4(n) =

[0054]

[0055] Note that, if signals from all the paths were up-sampled and added, they could be represented as

[0056] x-j(n) + x2(n) ’f

[0057]

[0058] which can still be easily separated using an FFT.

[0059] The first path may serve as the reference path, which means the phases of the other paths would be aligned with that of this reference path. The subcarriers in each of the transmit paths thus form a subset, which is technically orthogonal to that of the subcarriers in other paths and can be very easily separated in the frequency domain because of the very nature of OFDM. However, the data, and hence the phases of the subcarriers of the calibration symbol are kept random to keep the PAPR low. After using an I FFT (315) for each path, the time domain signals are upconverted through the different transmit paths simultaneously. During transmission, these signals are subject to various propagation effects, such as phase and amplitude variations caused by the physical characteristics of the antennas, board design constraints, and temperature variations. The orthogonality of the subcarriers ensures simultaneous transmission without interference, maintaining clear channels for each antenna path.

[0060] Feedback is collected via directional couplers (325) from each of the RF paths and is combined additively using a power combiner (320) and down-converted which reflects the aggregated behavior of all the sounded antennas. The subcarriers are separated in the frequency domain.

[0061] RxAnt1“ = a1X4keJ< P1

[0062]

[0063] RxAnt2 = FFT{A2x2n)e!<P^} = a2X4k+1eJ- R^Ant-i = FFT^x^nleW*} = a3X4k+2e^3

[0064]

[0065] Fx'AntA ~ F Fl {A4x4(n)ei<p4] - a4X4k+3e^4

[0066] Where a1, a2, a3, a4and φ1, φ2, φ3, φ4represent the gain and phase changes of the signal while traversing the calibration path.

[0067] Because the frequency domain data of the transmitted calibration symbol had random phases, the received subcarriers are multiplied by their respective conjugates (335), to make the feedback data independent.

[0068] This operation is represented mathematically as follows:

[0069] F

[0070]

[0071] BAntl= RxAM.* X4k=

[0072] FBAnt2= RxAnt2.* X'4k+1= a2ejφ2FBAnt3= RxAnt3.* X'4k+2= a3ejφ3

[0073] FBAnt4= RxAnt4.* X'4k+3= a4ejφ4

[0074] The phases of each of the resulting data-independent subcarrier subsets, corresponding to each path, may now be easily compared with that of the subcarriers from the designated reference path extracted from the same feedback signal. These subcarrier phases and amplitudes are compared with those of the reference path phase and amplitude to determine the necessary compensation factors.

[0075] Calibration for the remaining antennas w.r.t. the first (reference) antenna is given by

[0076] CalAnt2= (FBAnt1 / FBAnt2)' = (α1 / α2)ej(φ2−φ1)

[0077] α1 / α2

[0078] '■F&Ant2' a2

[0079] __ (FBAntl'

[0080] CdlAnl3■■■■ I ■””” ^±.eiF-p-.i~<pA

[0081] '■p aAnt3- 0-2

[0082]

[0083] ! *DAnti' tt-j ■ (

[0084] -4nt4 I p n IC

[0085]

[0086] aAnt4'a4

[0087] FIG. 3(A) illustrates a how a receive antenna calibration can be performed. In this configuration, a signal sent through a common transmit path is routed through a power divider (320B) to split the calibration signal across multiple receive paths. The received signals through individual Rx paths are then down converted and taken to frequency domain. The signal received through the reference path is multiplied by the conjugate of those from the other receive paths to derive the phase and amplitude difference. The conjugates of these factors serve as the correction factor for the receive antenna calibration.

[0088] The power divider used in this receive calibration setup may serve a dual purpose - it may function as a power combiner when the system is configured for transmit antenna calibration. This versatility in component functionality may allow for efficient switching between receive and transmit calibration modes, potentially simplifying the overall calibration architecture and reducing hardware complexity.

[0089] FIG. 3(B) illustrates how a subset of the antennas may be addressed at a time, to avoid spacing the allocated subcarriers too far apart in a path. For large MIMO systems (viz. ≥ 64 antennas), if the subcarriers are assigned to each path using the round-robin method, the spacing between the allocated subcarriers in each path becomes very high, and interpolation of coefficients for the missing subcarriers can be difficult. In such cases, the calibration is done sequentially addressing a smaller subset of antennas at a time. In an embodiment of the present invention, FIG. 3(B1) illustrates that not all antennas need to be addressed together, especially when the number of antennas is large. Here only Antenna 2 and Antenna 3 are calibrated against Antenna 1, the latter serving as the reference antenna. FIG. 3(B2) illustrates the last step of successive calibrations, showing the calibration of the (M-1)stAntenna and MthAntenna against the same reference Antenna 1. This approach maintains the allocated subcarrier separation in each path within a specified limit, ensuring orthogonality of calibration signals as the number of antennas increases. The use of a common reference antenna provides consistency across the entire array, minimizing cumulative errors and accommodating various array sizes from small configurations to massive MIMO systems.

[0090] FIG. 4 presents a detailed flowchart outlining the steps involved in the Tx calibration process (400) in accordance with one embodiment of the present invention. The flowchart systematically guides through each stage of the calibration procedure, starting from the initialization of calibration signals to the adjustment of transmission parameters. Each step is designed to fine-tune the transmission characteristics, ensuring optimal alignment and performance of the transmitting antennas.

[0091] At step 405, random data, corresponding to the full-band OFDM symbol is chosen and distributed in a round-robin method (410) among the transmit antennas to form the subcarrier subset, and one of the antennas is designated as the reference antenna. At step 405 of the transmitter calibration process, a frequency domain calibration symbol is chosen that spans the entire bandwidth of the communication channel

[0092] At step 410 of the transmitter calibration process, the primary reason to distribute the subcarriers into multiple transmit paths, is to let the signals travel through all the transmit paths, including the reference path side-by-side In this process, the subcarriers sent through the reference path, provide a baseline for comparison with other subcarriers to identify deviations in the other paths.

[0093] The existing beamformer is reused to distribute the calibration symbol subcarriers along specific paths by applying ones and zeros as weights to each subcarrier in each transmit path, this technique allows for the simultaneous transmission of both reference and sounding information for comparison of the phases and amplitudes of respective antenna signals in the common feedback path. The organized assignment of subcarriers helps ensure that reference signals follow the same designated reference paths as the sounding signals. This systematic distribution may facilitate measurement and analysis at the receiver, potentially leading to effective calibration and optimization of the antenna array.

[0094] At step 415 of the transmitter calibration process, the signals are converted from the frequency domain to the time domain and then transmitted through their designated paths. This step is crucial for preparing the signals for transmission and ensuring they are compatible with the antenna system. The conversion process involves using the Inverse Fast Fourier Transform (IFFT), which transforms the frequency domain signals, including the subcarriers, into a time-domain waveform.

[0095] To enhance signal integrity and to avoid synchronization complexities of the feedback signal mitigate inter-symbol interference (ISI), a cyclic prefix is added to the time-domain signal. The cyclic prefix is a copy of the end portion of the signal appended to the beginning, which helps preserve the orthogonality of the subcarriers and ensures the signal remains intact during transmission, especially in multipath environments.

[0096] Once the signals are formatted with the cyclic prefix, they are transmitted through their respective paths in the antenna array. The existing transmitter chain, including components such as up-sampling chains, crest factor reduction units, digital predistortion units, power amplifiers, and antenna ports, is used for amplification and conditioning of the signals.

[0097] At step 420 of the transmitter calibration process, feedback from all transmitted paths is collected. A feedback mechanism gathers the received signals through directional couplers. These couplers sample a portion of the transmitted signal without significantly affecting the main transmission, ensuring that the feedback accurately represents the transmitted signal. The collected feedback signals are then combined into a single signal using a power combiner, which aggregates data from multiple sources, allowing for a common receive path that undergo the same distortions and deviations for signal corresponding to all the paths. At step 425 the combined feedback signal undergoes processing, including down-sampling, filtering, and at step 430 a Fast Fourier Transform (FFT) is performed to extract information about phase and amplitude characteristics.

[0098] At step 430 of the transmitter calibration process, the focus is on converting the received signal into the frequency domain to facilitate easy separation of path specific signals for detailed analysis and calibration. The transformation into the frequency domain is accomplished using the Fast Fourier Transform (FFT), which ensures the orthogonality of the subcarrier subsets and hence the separability of signals of each antenna path from the combined signal, exposing the magnitude and phase characteristics of each frequency element of each antenna path within the combined feedback.

[0099] To maintain a low PAPR, the transmission of same signal through subcarriers is avoided. At step 435 of the transmitter calibration process, the focus is on dividing the received subcarriers by the respective transmitted subcarriers to remove the data-dependent phases and amplitudes. Therefore, the resulting signals received from different antennas may now be directly compared.

[0100] At step 440 of the transmitter (Tx) calibration process, the goal is to compare the phases and amplitudes by dividing the resultant subcarriers of the symbol by the reference subcarrier IQ of the same symbol. This step plays a critical role in generating frequency domain error factors, which give the calibration adjustments and is used to improve the overall system performance. The process begins by comparing the feedback subcarriers of the reference path with those of the rest. By doing this, the system quantifies the discrepancies among the paths, identifying errors or deviations in both amplitude and phase.

[0101] The division operation isolates these discrepancies, producing frequency domain error factors that are critical for determining the calibration adjustments. These error factors indicate the level of performance degradation in terms of amplitude and phase shifts. For instance, an amplitude mismatch would result in an error factor magnitude deviating form, while phase shifts are identified by a non-zero phase error. By evaluating these error factors, the system can calculate calibration coefficients, which are necessary to correct any misalignments. This step is usually part of an iterative process where the error factors are continuously assessed, and the calibration coefficients refined until optimal performance is achieved.

[0102] At step 445 of the transmitter (Tx) calibration process, the focus is on interpolating the frequency domain correction factors for the missing subcarriers. The measured correction factors are the conjugates of the error factors derived in the previous step. This step is crucial for deriving correction factors for subcarriers that were not directly measured by the calibration signal. The main goal of this step is to extend the calibration to all subcarriers, including the ones not explicitly covered by the calibration process. The interpolation process, which could be linear or involve more advanced methods like spline interpolation, etc., calculates these correction factors for the missing subcarriers based on the error factors of the neighboring subcarriers. This step is optional and may be required when the error factors are separated by large number of subcarriers. At step 450 of the calibration process, the focus is on multiplying the outgoing transmit data (post-beamforming) with the frequency domain correction factors for each subcarrier. This step is crucial for adjusting the transmit signal to account for any errors in amplitude or phase that were identified during the calibration process. The objective is to ensure that the outgoing signals are optimized for accurate and efficient transmission across all subcarriers. In this step, the outgoing transmit data is adjusted by multiplying with the correction factors to each subcarrier, ensuring that any identified errors in the frequency domain are compensated for, effectively improving the quality and integrity of the transmitted signal. The correction factors address both phase and amplitude errors, aligning the outgoing data with the calibrated state required for optimal transmission performance.

[0103] After this multiplication, the resulting signal is now properly calibrated and ready for transmission. The corrected signal will continue through the transmission chain, undergoing further processes like inverse Fast Fourier Transform (IFFT) to convert to the time domain before being sent through the antenna. This final calibrated signal ensures better communication performance, reducing distortions, and maintaining signal quality across the entire bandwidth.

[0104] In some aspects, a calibration method for an antenna array or multiple antennas in a wireless communication system may be implemented. The method may include configuring the system to transmit orthogonal subcarrier sub-sets of an OFDM calibration symbol simultaneously through multiple transmit antennas. These subcarrier sub-sets may be distributed across various transmit paths, with each sub- set carrying at least one non-zero subcarrier. In an example embodiment, the "non¬ zero subcarrier" refers to an active frequency component within an Orthogonal Frequency Division Multiplexing (OFDM) signal that carries information or energy. Specifically, it is a subcarrier within the OFDM symbol that has been modulated with data ora reference signal, as opposed to null subcarriers which carry no information. Further, in the context of this calibration method, a non-zero subcarrier contains calibration information or sounding signals used to measure and adjust the phase and amplitude characteristics of the transmit antenna paths. In an example, the presence of at least one non-zero subcarrier in each subcarrier subset ensures that meaningful calibration data is transmitted through each antenna path being evaluated, enabling the system to accurately assess and correct for path mismatches across the entire frequency band of interest.

[0105] Further, the method may involve collecting feedback of the transmitted signal from more than one antenna and combining this feedback into a single consolidated signal. This consolidated signal may then be down -converted and subjected to a Fourier transform operation. After the Fourier transform, the signal may be separated Into subcarrier sub-sets. These sub-sets may Include one subset from a reference path and other subsets from antenna paths that are undergoing calibration.

[0106] The method may further include dividing the subsets of subcarriers by the transmitted subcarrier subset. This operation may generate data-independent subcarriers, which can be useful for subsequent analysis. The phases and amplitudes of these data-independent subcarriers may be compared to identify any mismatches in the transmit paths. Based on these identified mismatches, the method may involve adjusting the phases and amplitudes of the transmission paths.

[0107] The ultimate goal of these adjustments may be to produce beams that improve the overall throughput of the wireless communication system. By fine-tuning the transmission characteristics based on the calibration results, the system may achieve more efficient and effective wireless communication.

[0108] In some aspects, the method of configuring subcarrier subsets may include non-zero subcarriers over a wide frequency range. This configuration may allow simultaneous calibration to be performed over large frequency bands used by the wireless communication system. The use of non-zero subcarriers across a wide frequency range may enable comprehensive calibration across the system's operational bandwidth.

[0109] The step of configuring subcarrier subsets may also involve assigning subcarriers over a wide frequency range. This assignment may facilitate simultaneous calibration across large frequency bands utilized by the wireless communication system. By distributing subcarriers across a broad spectrum, the method may achieve thorough calibration of the antenna array’s performance over its entire operational range.

[0110] When multiplying the feedback with the conjugate of the transmitted subcarrier subset, the method may aim to eliminate data-dependent phases introduced during transmission. Mathematically, a simple QPSK can be written as xt+ jy.- which may undergo some phase and amplitude change 0 and a, by the time it reaches transmit antenna and it can be represented as a(x. + jy^e^8

[0111] Multiplying the feedback with the conjugate of the corresponding transmitted signal results

[0112]

[0113] in + jyi)eje(xl- +yf2) = aejBsince xtand ytare both ±1 for QPSK.

[0114] Additionally, this step may help maintain a lower Peak-to-Average Power Ratio (PAPR) of the calibration symbol. By addressing these factors, the method may enhance the accuracy and efficiency of the calibration process.

[0115] The step of comparing phases may include calculating the difference of both amplitude correction factors and phase adjustment values for each transmit path. This calculation may contribute to ensuring precise alignment of the antenna array. By considering both amplitude and phase adjustments, the method may achieve a more comprehensive calibration of the antenna system.

[0116] In separating the received signal into subcarrier sub-sets, the method may divide the signal into a reference path and other paths undergoing calibration. This separation may be performed in a way that ensures no correlation or synchronization is involved in the calibration process. By avoiding the need for correlation or synchronization, the method may significantly reduce the complexity of the calibration procedure.

[0117] The above methodology may leverage existing 4G / 5G system infrastructure and protocols for calibrating the antennas, while not being limited to these specific technologies. By utilizing established cellular network frameworks, the calibration process can potentially benefit from mature signaling mechanisms, resource allocation schemes, and synchronization methods already in place. However, the approach may be adaptable to other wireless communication standards, both current and future. The calibration technique could be applied to various antenna array configurations and may be extensible to emerging technologies like 6G or other advanced wireless systems. This flexibility allows the method to evolve alongside advancements in wireless communication, potentially offering a scalable solution for antenna calibration across different generations of mobile networks and beyond.

[0118] FIG. 5 is an example illustration comparing antenna beams before and after the calibration process, highlighting the improvements achieved through the calibration method described in the invention.

[0119] In one embodiment, the beams before calibration are depicted as having irregular shapes and directions, indicating that the antenna system is not optimally aligned. This misalignment can lead to suboptimal performance, such as reduced signal strength, increased interference, and overall lower throughput in the communication system.

[0120] After the calibration process, the beams are shown to be more uniform and directed, demonstrating that the calibration has successfully compensated for any phase and amplitude mismatches among the antennas. The calibration process aligns the beams to the desired directions, ensuring they are focused and optimized for maximum coverage and signal quality.

[0121] The clear distinction between the pre-calibration and post-calibration beams underscores the effectiveness of the calibration method. This visual representation serves to illustrate the tangible benefits of implementing the proposed antenna calibration techniques in real-world applications.

[0122] FIG. 6 is a block diagram illustrating an example of a schematic hardware configuration of the network node according to embodiments of the present disclosure. Referring to FIG.6, the network node 600 includes a network interface 610, a processor 620, a memory 630, and a storage 640. The network interface is, for example, a network adaptor, and transmits signals to and receives signals from the network. The processor performs processing on signals that are transmitted and received via the network interface. The processor may include a plurality of processors or may be a single processor. The memory stores a program to be executed by the processor, parameters related to the program, and data related to the program. The memory may include at least one of a ROM, an EPROM, an EEPROM, a RAM, and a flash memory. All or part of the memory may be included in the processor. The storage stores various information. The storage may include at least one of an SSD and an HDD.

[0123] Figures are merely representational and are not drawn to scale. Certain portions thereof may be exaggerated, while others may be minimized. Figures illustrate various embodiments of the invention that can be understood and appropriateiy carried out by those of ordinary skiii in the art.

[0124] In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.

[0125] It is understood that the above description is intended to be illustrative, and not restrictive. It is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined in the appended claims. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively.

Claims

We Claim:

1. A calibration method for an antenna array or multiple antennas in a wireless communication system, the method comprising:configuring to transmit orthogonal subcarrier sub-sets of an OFDM calibration symbol simultaneously through a plurality of transmit antennas, where the subcarrier sub-sets may be distributed to multiple transmit paths, each sub-set carrying at least one non-zero subcarrier;collecting feedback of the transmitted signal from more than one antenna and combining the feedback into one consolidated signal;down-converting the consolidated signal through a common receive path and performing a Fourier transform on the down-converted signal;separating the resulting frequency domain signal into subcarrier subsets, which may include one subset from a reference path and other subsets from antenna paths to be calibrated;dividing the subcarrier subsets by the corresponding transmitted subcarrier subsets to remove data dependence from the feedback subcarriers;comparing phases and amplitudes of the data-independent feedback subcarriers to identify transmit path mismatches; andadjusting transmission path phases and amplitudes based on the identified mismatches to produce beams for improved throughput.2 / 2. The method of claim 1, wherein the step of configuring subcarrier subsets include non-zero subcarriers over a wide frequency range, allowing the simultaneous calibration to be performed over large frequency bands used by the wireless communication system.

3. The method of claim 1, wherein the transmitting of orthogonal subcarriers is done by distributing the subcarriers using a beamforming circuit, which when not running the antenna calibration, applies appropriate beam weights to maximize coverage or throughput.

4. The method of claim 3, wherein the beamforming circuit applies appropriate multiplying factors for each subcarrier of each transmit path, functioning as a distribution unit of subcarriers into multiple simultaneous transmit antennas during calibration.

5. The method of claim 1, wherein the step of configuring further include directional couplers to capture feedback, wherein the feedback signal is used exclusively for calibration without affecting the main transmission.

6. The method of claim 1, wherein the step of combining further including optimizing to operate over a wide frequency range, allowing the calibration to be performed over large frequency bands used by the wireless communication system.

7. The method of claim 1, wherein the step of eliminating data-dependent subcarrier phases introduced during OFDM symbol transmission as otherwisesending same data in adjacent subcarriers means increased Peak-to-Average Power Ratio (PAPR) of the calibration symbol.

8. The method of separating the received signal into subcarrier subsets into reference path and other paths that are undergoing calibration, ensuring that no correlation or no synchronization is involved in the calibration, reducing complexity significantly.

9. The method of claim 1, wherein the step of compensating including calculating the difference of both amplitude correction factors and phase adjustment values of each transmit path, ensures precise alignment of the antenna array.

10. The method of claim 1, wherein one of the existing receive paths serves as the common path to collect the combined feedback during transmit antenna calibration, and further one of the existing transmit paths serves as the common path to transmit during receive antenna calibration, thus avoiding extra circuits, further, the existing beamforming circuit Itself Is used to distribute the subcarrier subsets onto different transmit paths.

11. The method of claim 1, wherein the calibration signals from multiple antennas are combined using a power combiner, which is realized using the same power divider of the receive antenna calibration circuit operated in the reverse direction with appropriate switches.

12. The method of claim 1, further comprising: transmitting calibration signals on at least two antenna paths simultaneously, to let one of them act as the referencefor easy comparison of the received signals; and repeating the process for the remaining paths until all antennas in the array are calibrated.

13. A network node in a wireless communication system, the network node comprising:a processor and a memory, the processor is configured for:configuring to transmit orthogonal subcarrier sub-sets of an OFDM calibration symbol simultaneously through a plurality of transmit antennas, where the subcarrier sub-sets may be distributed to multiple transmit paths, each sub-set carrying at least one non-zero subcarrier;collecting feedback of the transmitted signal from more than one antenna and combining the feedback into one consolidated signal;down-converting the consolidated signal and performing a Fourier transform on the down-converted signal;separating the resulting frequency domain signal into subcarrier sub-sets, which may include one subset from a reference path and other subsets from antenna paths to be calibrated;multiplying the subcarrier subsets by conjugates of the transmitted subcarrier subsets to remove data dependence from the feedback subcarriers:comparing phases and amplitudes of the data-independent feedback subcarriers to identify transmit path mismatches; andadjusting transmission path phases and amplitudes based on the identified mismatches to produce beams for improved throughput.

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